1. Field of the Invention
The present invention relates to a machine for inserting a cathode of a cathode-ray tube.
2. Description of the Prior Art
Machines currently used to insert the electron gun cathodes of cathode-ray tubes generally use complicated and slow instruments, which maintain requisite precision with difficulty, in order to measure the distance between the active face of these cathodes and the grid 1 (or, as the case may be, the grid 2). These machines position the cathode with respect to the grid 1 by first interposing a sensor of fixed length between the cathode and the grid 1, the cathode being placed on a fixed support and the gun on a moving support driven by a roller that works with a cam-shaped groove of a leading screw which is itself driven by a stepping motor.
A first shoulder of this groove determines the position for measuring and setting the position of the cathode, then the gun is drawn back, the sensor is released and the gun is moved forward by a distance equal to that by which it has been moved back plus the length of the sensor, and reaches the position where the cathode is to be soldered in the gun eyelet, this position being also determined by a shoulder of the groove. Thus, any change in the setting of the machine requires the disassembling of the sensor and its re-machining according to new dimensions. The driving device, using a leading screw and roller, is hardly precise: the groove of the leading screw should be completely free of dust or debris and this is difficult to obtain in industrial manufacturing conditions. Even if the stepping motor stops precisely in the desired angular position, the device for coupling with the leading screw which drives it has backlashes which are difficult to take into account. The forces exerted on the roller, both by the gun carriage and the leading screw cause the backlashes of this transmission of motion to be reflected in the carriage.
An object of the present invention is an automatic, fast, precise, reliable and simple machine for the insertion of cathodes in a cathode-ray tube gun.